#include "bits/stdc++.h"
using namespace std;
#ifdef _DEBUG
#include "dump.hpp"
#else
#define dump(...)
#endif

#define int long long
#define rep(i, a, b) for (int i = (a); i < (b); i++)
#define rrep(i, a, b) for (int i = (b)-1; i >= (a); i--)
#define all(c) begin(c), end(c)
const int INF =
    sizeof(int) == sizeof(long long) ? 0x3f3f3f3f3f3f3f3fLL : 0x3f3f3f3f;
const int MOD = (int)(1e9) + 7;
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return true;
  }
  return false;
}

signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  freopen("B-small-attempt0.in", "r", stdin);
  freopen("B-small-attempt0.txt", "w", stdout);
  // freopen("in.txt", "r", stdin);
  // freopen("out.txt", "w", stdout);
  int T;
  cin >> T;
  cout << fixed << setprecision(10);
  for (int t = 0; t < T; t++) {
    string ans;

    int N;
    cin >> N;
    int R, O, Y;
    cin >> R >> O >> Y;
    int G, B, V;
    cin >> G >> B >> V;

    int maxi = N / 2;
    if (R > maxi || Y > maxi || B > maxi) {
      ans = "IMPOSSIBLE";
    } else {
      using P = pair<int, char>;
      vector<P> v;
      v.emplace_back(R, 'R');
      v.emplace_back(Y, 'Y');
      v.emplace_back(B, 'B');
      sort(all(v));
      reverse(all(v));
      vector<string> p;
      rep(i, 0, v[0].first) { p.emplace_back(string(1, v[0].second)); }
      int cur = 0;
      rep(i, 0, v[1].first) { p[(cur++) % p.size()] += v[1].second; }
      rep(i, 0, v[2].first) { p[(cur++) % p.size()] += v[2].second; }
      // dump(p);
      rep(i, 0, p.size()) { ans += p[i]; }
    }
    cout << "Case #" << t + 1 << ": " << ans << endl;
  }
  return 0;
}